Electric fuse and indicator



Jan. 30, 1940- w. K. RANKIN ELECTRIC FUSE AND INDICATOR Filed April 29, 1938 Patented Jan. 30, 1940 UNITED STATES PATENT OFFICE William K. Rankin,

Lansdowne, Pa., assignor to General Electric Company, a corporation of New York Application April 29, 1-938, Serial No. 205,105

12 Claims.

The present invention relates to improvements in electric fuses,-more particularly of the enclosed type, and indicating means therefor.

In the development of power fuses for interruption of currents of large magnitude without noise, discharge of solid or liquid particles, or production of gases which must be either discharged to atmosphere or dissipated in a high pressure chamber, difiiculties have been encountered in providing suitable enclosures and fuse operation indicating means which do not render the fuses subject to contamination or escape of gases.

It is an object of the present invention to provide improved housing and indicating means employable for overcoming the above mentioned dimculties in fuses of the character referred to.

and in other applications where-problems of a similar nature are encountered.

One of the more specific objects of the invention is the provision of a substantially gastight sealing closure for the casing of an enclosed fuse, which closure embodies means arranged to give indication of fuse operation without impairment of the casing seal.

Another object of the invention is the provision of an improved form of indicating device operaible by gas pressure in response to fuse operat on.

Other objects and the details of that which I believe to be novel and my invention will become apparent from the following description and the claims appended thereto, taken in conjunction with the accompanying drawing in which Fig. 1 illustrates in longitudinal section an exemplary fuse construction with one form of combined closure and indicating means embodying the present invention; Fig. 2 is an end view of the fuse of Fig. 1 showing the indicating means after operation; Fig. 3 illustrates in longitudinal section a modified form of closure and indicating means embodying the invention; and Fig. 4 illustrates details of the construction and operated appearance of the indicating means of Fig. 3.

The exemplary fuse illustrated in Fig. 1 is of the current limitingmype and incorporates a plurality of fusible conductors l0 spirally wound on a supporting core II and embedded in an interrupting medium l2, such as sand, relatively finely divided quartz or like material, which is inert,

or non-gas producing at the arc temperatures likely to be encountered upon fuse operation. Core II is comprised of high temperature resisting ceramic material and is constructed in star-shaped form with a central bore I: for a purpose which will become apparent hereinafter. Conductors I0 are connected in parallel between terminal bands l4 and I5 mounted respectively on opposite ends of the core. Small sections of the conductors intermediate their ends are enclosed in beads l6 of ceramic material which provide thermal chambers and serve to isolate the enclosed sections of the conductors from the interrupting medium 12. Thus heat radiation from the enclosed sections of the conductors is retarded as compared with heat radiation from those portions of the conductors which are in contact with the interrupting medium, so that fusion of the conductors at the enclosed sections is insured upon low current.

The parts above described are enclosed in a tubular casing l1 which is illustrated as being constructed of glass, although it may be constructed of fibre or other material having the required dielectric and mechanical strength, and which casing has metallic ferrules 20 and 2| secured respectively on opposite ends thereof by means of a suitable metal-to-glass seal, as indicated at 22. For convenience, these ferrules 20 and 2| will be designated hereinafter as the upper and lower ferrules respectively, since the fuse illustrated is adapted to be mounted in such position that ferrule 2| is lowermost in order that the indicator, hereinafter described, may be observed readily from the ground. However, it is to be understood that my invention is not limited to any particular positioning of the fuse. Terminal bands l4 and I5 are connected respectively to ferrules 20 and 2| by connection strips 23 which are formed integrally with the connection bands and which have their ends connected to the ferrules by soldering or welding. The upper end of ferrule 20 is closed by means of a tight fitting metal disk 24 which provides a substantially gas-tight seal for the upper end of the fuse enclosure.

The lower end of the fuse housing is closed by means of a relatively stiff partition member 25 and a flexible disk 26, which latter is adapted to serve as an indicator or target in a manner to be described hereinafter. Disk 26 is comprised of a thin imperforate sheet of metal, such as copper, and has an inwardly projecting peripheral flange 21 which is soldered, welded, or otherwise secured to the inner surface of ferrule 2 l in a manner to provide a gas-tight sealed junction between the disk and the ferrule. Thus the central portion of the disk constitutes a dia- "phragm which is free to flex inwardly and outwardly. Partition member 25, which also is comprised of metal, such as copper, is disposed on the inner side of disk 26 and is soldered, welded, or otherwise secured to flange 21 in a manner to provide a gas-tight sealed junction between the disk and'the partition member. The partition member is cupped inwardlyso as to provide a cavity for accommodating the central or diaphragm portion of the flexible disk when the latter is in its inwardly retracted or non-indicating position shown in full lines in Fig. 1.

For effecting operation of disk 26, there is provided a charge 30 of a material, such as smokeless powder, capable of generating gas upon being ignited or heated to a sufficiently high temperature. This charge is accommodated in a chamber provided by a centrally located inwardly projecting thimble 3| formed in partition member 25. Ignition of the charge is effected on fuse operation by means of an indicator wire 32 which is disposed in the central bore |3 of core and which has one end connected to the upper terminal band l4. The other end of this wire extends through thecharge in thimble 3| and terminates between two thin sheets 33 of insulating material, such as tissue paper, arranged between partition member 25.and disk 26. At the point where wire 32 passes through the wall of thimble 3|, it is molded into a stem 34 of glass or other suitable insulating material and a sealed Junction between this stem and thimble 3| is eflected by means of a body of cement 36. Thus the lower end of the indicator wire is isolated electrically from the ends of the fusible conductors and the terminal at the lower end of the fuse so that it does not carry current under normal conditions.

Upon rupture of fusible conductors ||I due to excess current, a potential is established between the lower end of indicator wire 32 and the lower terminal structure of the fuse, which potential produces arcing between the end of the indicator wire and either partition 25 or disk 26. This areing and the burning back of the indicator wire causes ignition of charge 30 with resultant generation of gases the pressure of which causes dia-@ phragm 26 to reverse from its position illustrated in full lines to its position illustrated in broken lines in Fig. l. The amount of material used in charge 30 is carefully determined so that the amount of gas produced will be sufficient to cause reversal of the diaphragm but will not cause rupture of the sealed enclosure or chamber provided by partition 25 and disk 26. Preferably the target or diaphragm portion of disk 26 is given 7 a coating of paint of some conspicuous color, and a legend, such as Blownf as indicated at 38 in Fig. 2, is applied thereto in a contrasting color. When the diaphragm is in its normal inwardly retracted position, it is hidden, in the embodiment of Fig. 1, by a relatively inflexible disk 39 of paper, Celluloid, or the like, which is painted with some relatively neutral color and which is attached to diaphragm 26 by paint, glue, or other suitable adhesive around its periphery, as indi cated at 40. This disk is ejected when diaphragm 26 reverses its position so as to reveal the diaphragm and its legend, as shown in Fig. 2. Subsequent to reversal of diaphragm 26 the gases in the chamber formed by this diaphragm and partition 25 quickly cool so that no appreciable pressure is left under the diaphragm.

In the modification somewhat diazrammatically illustrated in Fig. 3, only a single fusible conductor 43 is employed, wound upon an insulating supporting core 44 and disposed within an insulating casing 45, illustrated as being of glass,

to the lower end of which is secured a metallic ferrule 46 by means of a suitable metal-to-glasa seal indicated at 41. It is contemplated that casing 45 be filled with some form of arc extinguishing material such as that previously described in connection with the embodiment of Fig. 1. The cup-shaped relatively member 48 and the flexible metallic disk 43 which serve to close the lower end of the fuse enclosure are held in place by crimping over the end of ferrule 46, as indicated at 50, in such manner as to form a sealed junction around the peripheries of the disk and partition member. A charge 5| of smokeless powder or the like is disposed in a thimble-shaped portion 62 of partition member 48 and is partially enclosed by an insulating capsule 53 which serves to isolate the charge from the interior of casing 46.

In the embodiment of Fig. 3, the fusible conductor 43 itself extends into the charge 6| and has its end connected by soldering or welding to partition member 48, as indicated at 54, the portion of the conductor passing through the partition member being tightly engaged by capsule 53 so as to maintain the isolation between the charge and the interior of casing 46. A connector 55 is provided for insuring good electric connection between ferrule 46 and thimble 62 adjacent the point of connection of conductor 43.

The outer surface of the diaphragm or target portion of disk 49 preferably is provided withza coating 56 of relatively flexible paint of some bright color, such as red, and has applied thereto also a legend such as Blown as indicated at 61, this legend being in a contrasting color, such as black. The surface of the diaphragm has applied thereto also a coating 58 of brittle enamel in some neutral color, which coating 58 serves normally to conceal coating 56 and legend 61 when disk 49 is in its inwardly retracted position.

Upon passage of excess current through fusible conductor 43, charge 5| becomes suiflciently heated, or ignited, to generate a gas the pressure of which causes reversal of diaphragm 49 to its position illustrated in broken lines in Fig. 3. With reversal of the diaphragm, brittle coating 58 isshattered, as indicated in Fig. 4, so as to reveal the conspicuously colored surface of the diaphragm and legend 51.

will be apparent from the foregoing description, an important feature of the combined closure and indicating means of the present invention is that isolation of the interior of the fuse "enclosure from atmosphere is maintained thereby, both prior to and after fuse operation. This prevents oxidation of the fusible conductors and contamination of the arc-quenching material and other elements within the fuse enclosure, thereby insuring proper fuse operation even after long periods of service. Also, none of the gases from the charge of gas-producing material is permitted to enter the fuse enclosure to impair the effectiveness of current interruption upon fuse operation. A further advantage is that such gases as are produced within the fuse enclosure as a result of fuse operation are prevented from escaping to atmosphere to cause possible ignition of adjacent inflammable materials or damage to adjacent apparatus.

What I claim as new and desire to secure by stiff metallic partition an indicator element movable from a normal position to an indicating position in response to pressure in said chamber, means operable for developing pressure in said chamber, and means for effecting operation of said pressure developing means in response to fuse operation.

2. In an electric fuse, the combination with an enclosing casing having an opening and a fusible element in said casing, of partition means gastightly sealing said opening, means exteriorly of and cooperative with said partition means to provide a chamber gas-tightly sealed off from the interior of said casing and having an indicator element movable from a normal position to an indicating position in response to gas pressure in said chamber gas producing means in communication' with said chamber, and means operable in response to fuse operation for causing said gas producing means to develop pressure in said chamber.

3. In an electric fuse, the combination with an enclosing casing having an opening and a fusible element in said casing, of partition means gas-tightly sealing said opening, means including a flexible diaphragm exteriorly of and cooperative with said partition means for providing a gas-tight chamber sealed off from the interior of said casing, which said diaphragm is arranged to flex from a normal position to an indicating position in response to gas pressure in said chamber, gas producing means communicating with said chamber and operable for producing pressure in the chamber, and means responsive to fuse operation for effecting operation of said gas producing means.

4. In an electric fuse, the combination with an enclosing casting having an opening and a fusible element in said casing, of means including a partition member substantially gas-tightly closing said opening, which said member has a cupshaped portion providing an outwardly facing cavity, means cooperative with said member to provide exteriorly of the member a chamber substantially gas-tightly isolated from the interior of said casing, said last mentioned means including a flexible diaphragm normally reposing in said cavity, and means responsive to fuse operation for producing in said chamber a pressure suflicient to cause flexure of said diaphragm outwardly to an indicating position.

5. In an electric fuse, the combination of an enclosing casing having an opening, a fusible element in said casing, means including a partition member substantially gas-tightly closing said opening, means including a flexible diaphragm exteriorly of said partition member cooperative with said member to provide a chamber substantially gas-tightly isolated from the interior of said casing, a charge of gas producing material carried by said partition member in communication with said chamber, and means responsive to fuse operation for causing said material to produce a gas pressure in said chamber, said diaphragm being movable from a normal position to an indicating postion in response to pressure in said chamber.

6. In an electric fuse, the combination of an enclosing casing, spaced terminals, means providing a chamber gas-tightly sealed off from the interior of said casing, said means including a flexible diaphragm operable from a normal position to an indicating position by gas pressure in said chamber, gas producing material communicating with said chamber for producing pressure therein, and a conductor connected between said terminals and having a. fusible section in said casing, said conductor having a portion extending in heat transfer relation with said material.

7. In an electric fuse, the combination of an enclosing casing, spaced terminals, a conductor connected between said terminals and having a fusible section in said casing, means including a flexible diaphragm providing a chamber gastightly sealed ofi from the interior of said casing, said diaphragm being operable from a normal position to an indicating position by gas pressure in said chamber, gas producing material communicating with said chamber for producing pressure therein, an. auxiliary conductor having one end connected with one of said terminals, the other end of the auxiliary conductor being normally electrically isolated from the other of said terminals, and means cooperative with said other end of the auxiliary conductor for producing an arc in proximity with said gas-producing material upon rupture of said first mentioned conductor.

8. In an electric fuse, the combination of an enclosing casing having an opening, spaced terminals, means including a partition member substantially gas-tightly closing said opening, means including a flexible diaphragm member exteriorly of and cooperative with said partition member to provide a chamber substantially gas-tightly isolated from the interior of said casing, gas producing material operable for producing pressure in said chamber to effect movement of said disphragm member from a normal position to an indicating position, at least one of said members being of electric conductive material and electrically connected with one of said terminals, and a conductor electrically connected between said one of said members and the other ofsaid terminals, said conductor having a fusible section in said casing and a portion extending in heat transfer relation with said gas producing material,

9. In an electric fuse, the,combination of an enclosing casing having an opening, spaced terminals, a fusible conductor in said casing connected between said terminals, means including a partition member substantially gas-tightly closing said casing opening, means including a flexible diaphragm member exteriorly of and co-,- operative with said partition member to provide a chamber substantially gas-tightly isolated from the interior or said casing, gas producing material operable for producing pressure in said chamber to effect movement of said diaphragm member from a normal position to an indicating position, at least one of said members being of electric conductive material and electrically connected with one of said terminals, and an auxiliary conductor having one end connected with the other of said terminals, the other end of the auxiliary conductor being normally electrically isolated from said one terminal and extending into said chamber into position for cooperation with said one of said members to produce an arc in proximity with said gas producing material upon rupture of said first mentioned conductor.

10. In an electric fuse, the combination with a tubular casing having an open end and a fusible conductor in said casing, of a partition member and a flexible diaphragm, means securing said member and said diaphragm in substantially gastight closing relation to said open end of the casing, said diaphragm being arranged exteriorly of and cooperating with said member to provide a substantially gas-tight chamber, said member be- 76 indicating position, means for rendering the outer surface of the diaphragm conspicuous when in indicating position, and a coating of brittle material applied to the outer surface of the diaphragm for concealing said last mentioned means when the diaphragm is in its inward position, said brittle coating being arranged to shatter so as to reveal the outer surface of the diaphragm upon outward flexure or the dia- P rasm- 12. In an electric circuit interrupter, the combination of casing means providing a sealed enclosure and having spaced terminals, means in said sealed enclosure operable to interrupt an electric circuit, means providing'a chamber gastightly sealed off from said enclosure and having an element movable from a first position to a second position in response to pressure in said chamber, gas-producing means communicating with said chamber and operable to produce pressure in the chamber, and means operable responsively to operation of said circuit interrupting means for effecting operation of. said gasproduc'ing means.

WILLIAM K. RANKIN. 

